A variety of tools are commonly used for tensioning a loop of metal or thermoplastic strapping around materials disposed upon a pallet, around a bale of material, around a package, or around other objects. Typically, a loop is first formed around the object. Next, the overlapping portions of the strap are engaged by means of the tool so as to tension the loop, and then the overlapping strap portions are joined together by means of the tool.
For some applications, it is desirable to tension the loop to a predetermined tension force. Various manual and automatic tools that have been proposed and/or that are commercially available include tension control mechanisms for terminating the tension at the desired level.
However, while many of these tools may normally function well in the applications for which they were originally intended, the tension control systems can add undue complexity to the tool. The complexity is typically manifested by means of an increased number of parts which are susceptible to failure or improper operation under typical field conditions involving careless or inexperienced operators and dirty operating environments which can clog or otherwise adversely affect the proper operation of the tension control mechanisms.
Accordingly, it would be desirable to provide an improved tension control mechanism that could be incorporated within a tool with a reduced number of parts and that would be less susceptible to operational failure or improper operation.
In some applications it is desirable to use thermoplastic strapping, and it would be beneficial if an improved tension control mechanism could be employed that would operate effectively with such thermoplastic strapping.
In some applications there is also a need to only develop a very low degree or level of tension within the loop, at least initially. For example, there are applications wherein highly compressible material is compressed within large presses so as to form bales, and the bales, while still compressed within the presses, are then encircled with strapping. In some cases the strapping is fed through means of channels defined within the press, and a number of such straps are longitudinally arranged along the length of the bale within the press.
Before the press is released, it is desirable to pull each strap loop so that it just touches the bale surface. Next, the overlapping strap portions of each loop are joined together, and the bale press is released so as to allow the bale to expand against the encircling strap loops.
In order to prevent overloading any one of the strap loops disposed around the bale, it is desirable, to the extent possible, to insure that each one of the loops disposed around the bale is substantially the same size as the other loops and is therefore subjected to substantially the same expansion (tension) forces as each one of the other strap loops. In order to insure that each strap loop has approximately the same size as the other loops before the press is released, it is necessary that a means be found so as to ensure that each one of the strap loops is effectively pulled out of the press channels and into contact with the surface of the compressed bale.
In order to make sure that a particular strap loop is pulled completely free of the encircling channel defined within the bale press, and in order to insure that the strap is in contact with the surface of the bale over the entire periphery of the bale, it has been determined that a predetermined nominal amount of tension should be applied to each strap loop. It is contemplated that for some large bale press applications, a nominal degree of tension of approximately 100 pounds force tension within the strap loop would be sufficient so as to insure that the strap loop is in contact with the entire periphery of the compressed bale before the press is released.
The tension force of approximately 100 pounds would be relatively low when compared to the compressibility of the already highly compressed bale. Thus, there would be no possibility that any substantial further compression of the bale would result from the development of the 100 pound tension within the strap loop.
Because no further substantial compression of the bale would occur when subjected to the relatively low, 100 pound force tension, the size of the loop disposed around the compressed bale would be substantially equal to the peripheral extent of the bale before the loop was tensioned around it to the 100 pound tension level. Thus, each one of the strap loops disposed upon the compressed bale should have a size equal to the peripheral extent of the compressed bale, and all of the loops should therefore be of substantially the same size. Therefore, when the bale press is released, all of the strap loops should be subjected to substantially the same maximum tension force.
It would be desirable to provide an improved tension control mechanism that would operate at relatively low strap tension forces so that such a mechanism could be employed within tools for tensioning and joining the strap loops about compressed bales as discussed above.
Furthermore it would be advantageous if such an improved tension control mechanism could be used effectively with thermoplastic strapping, including polyester strapping which can be optimally used in connection with the above-discussed compressed bale applications.